Variable star V708 Car has an unusual chemical composition, study finds

A world crew of astronomers has carried out spectroscopic observations of a variable star often known as V708 Automobile. Outcomes of the observational marketing campaign, reported in a paper printed February 20 on the pre-print server arXiv, point out that this star has an uncommon chemical composition.

Cepheid variables (or Cepheids) are luminous, yellow, horizontal department stars altering their brightness with time because of common stellar pulsations. Provided that their intervals of variation are carefully associated to their luminosity, astronomers use them to measure interstellar and intergalactic distances.

Classical Cepheids, also referred to as Inhabitants I Cepheids, bear pulsations with very common intervals on the order of days to months. Provided that their pulsation and stellar parameters are strictly linked, these variables are additionally used as a testbed for stellar evolution theories.

Positioned about 14,350 light years away from the Earth, V708 Automobile is an enormous long-period classical Cepheid. Earlier observations have discovered that it’s a supergiant star with a mass of some 12 solar masses, pulsation interval of roughly 52.4 days (which will increase at a fee of 52 seconds per yr), and its luminosity is at a stage of 18,400 solar luminosities.

Nonetheless, though V708 Automobile has been recognized for 20 years, it stays a poorly studied variable. That’s the reason a gaggle of astronomers led by Valery V. Kovtyukh of the Odessa Nationwide College in Ukraine, determined to conduct a spectroscopy of this star utilizing the Excessive Decision Fiber échelle Spectrograph (HRS) on the Southern African Giant Telescope (SALT).

All in all, HRS allowed the crew to derive abundances of 27 chemical parts for V708 Automobile. The outcomes present that this star is lithium wealthy, which is mostly uncommon amongst supergiant Cepheids, as thus far solely six such objects have been recognized. The effective temperature of V708 Automobile was measured to be 5,206 Okay, whereas its metallicity was estimated to be at a stage of -0.4 dex.

By analyzing the collected information, it was discovered that V708 Automobile has an anomalous chemical composition. It turned out that the measured abundances of the chemical elements present a transparent correlation with their condensation temperature—the upper the condensation temperature, the decrease the abundance. The authors of the research suppose that such an anomaly could also be a results of dust–gasoline separation within the envelope (or prolonged environment) of the star.

“Via this mechanism, refractory parts kind dust grains within the envelope which can be swept out of the envelope by the radiative strain of the star. The gaseous fraction, enriched in risky parts, is accreted by the star, and finally, its environment acquires the noticed peculiarity,” the researchers defined.

The astronomers added that the observations in all probability caught V708 Automobile at a really short-term evolutionary stage of interplay with the shell.

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